Process for the production of ageresisting iron and steel



Patented Aug. 14, 1934 v PATENT OFFICE PROCESS FOR THE PRODUCTION OF AGE- BESISTING IRON AND STEEL cm Wallmann, Fritz Halbrock, and Emil Kampmann, Mnlheim-on-the-Buhr, .Germany No Drawing.

No. 620,309. In

This invention relates to a process for the production of age-resisting iron and steel.

It is known to produce age-resisting iron or steel, that is to say, iron or steel which, on'ageing, do not exhibit any substantially increased brittleness in suitable test pieces. Up to the present, it has been possible to produce such iron and steel in diiferent ways. The age-resisting property is obtained, for example, by treating the iron or steel with desoxidizing agents, during the melting and the maintenance of definite conditions, to a larger extent than is otherwise customary in melting ordinary kinds of iron and steel. Another way of obtaining the age-resisting property consists of a normalizing heat treatment (quenching and annealing) and also in hot working at temperatures in the vicinity of the upper transformation point. Finally, the age-resisting property can also be imparted by'alloying with certain metals, such as chromium, nickel, copper and the like.

All these processes increase, to a certain extent, the cost of the articles that are to be manufactured from age-resisting iron or steel, because they all entail operations additional to the ordinary manufacturing operations, thereby naturally increasing the cost ofthe finished products.

This is particularly the case when the age-resisting property is obtained by alloying, special heat treatment, and shaping within special ranges of temperatures.

Moreover, when known desoxidizing agents, such as aluminium, are employed, inclusions (in that case, of alumina) may be formed, which remain in the iron and steel and may cause, on their surfaces of fracture, defective places which render the employment of the piece questionable. As a rule, the desoxidizing agent employed for the production of age-resisting steels by extensive desoxidation, is added in the furnace, shortly before tapping, or else, after tapping, in the ladle. For this reason, in many instances, only a very short time is available for the desoxidation and it then easily happens that the intended ageresisting property of the steel is not obtained, this result being equivalent to a wasted charge.

Another defect arising in the production of age-resisting kinds of iron and steel, and also those in which that property is not required, is the circumstance that the slag of the molten bath,

Application June 30, 1932, Serial January 22, 1932 ving the desired capacity for absorbing sulphur co and phosphorus, being thereby formed.

Among the constituents which pass, contrary to desire, into this basic slag, is (inter alia) the manganese in the charge. In the most usual manner of conducting the melting process, it is 5 the practice to replace the manganese which has passed into the slag, and therefore become lost to the bath, by adding fresh manganese (in the form of ferro-manganese) to the bath towards the end of the process compensating for that manganese which has gone into the slag, thereby becoming useless for the bath, in order to obtain the desired end product.

However, as with the aforesaid addition of desoxidizing agents, such as aluminium, the addition of term-manganese towards the end of the melting process, gives rise to defects in the form of inclusions of manganese sulphide and manganese silicate-derived from the ferro-manganese-which inclusions may remain in the solidifying iron or steel, and impair its usefulness. In addition to the aforesaid inconveniences, the addition of term-manganese towards the end of the melting process, in the manner now generally employed in the melting operation in the Se mens-Martin process, considerably increases the cost of the product.

On this account, attempts have been made to recover the manganese from the slag by the addition of welding slag and iron oreor in some cases, only one of these agents-to the molten charge.

Said processes are, however, accompanied by several drawbacks. The addition of iron ore or welding slag introduces additional oxygen into 5 the bath, and experience shows that the removal of this oxygen is necessary and desirable. Moreover, it is doubtful whether, in adding lime after the ore and at a time when the temperature of the bath is very high, the part ascribed to the lime of absorbing sulphur and phosphorus from are produced, the rapidity of the reaction in- I. tended to take place between the slag and. the

bath being thereby unfavourably affected. It is therefore necessary, in many cases, to add fluorspar to these viscous slags, in order to improve their fluidity and thus assure the desired rapidity of the reaction.

The difliculties occurring in the above processes are excluded by the process according to the present invention, and the advantages aimed at in the aforesaid known process-such as reduction of cost by lowering the addition of ferro-manganese, and obtaining age-resisting iron or steel without the excessive employment of desoxldizing agents liable to lead to inclusions-are assured in a manner that is easily carried out in practice.

In the process of the present invention the early stage is carried through in the usual known As is customary in the pig and scrap or iron ore process, the charge is proportioned, so as to bear in mind the desired end figures for manganese, carbon and so forth, and is mixed with a sufllcient amount of lime to meet the requirements of the entire process. The whole can then be melted down, in any ordinary Siemens- Martin furnace, in the usual way, the abundant addition of lime forming a basic Martin slag. The abundant proportion of lime in the charge is able to exert a favourable action, especially at the low temperature of the first stage of the melting process, inasmuch as a more and extensive refining, in respect of sulphur and phosphorus, is thereby effected than if the lime were introduced at a later stage of the process.

When the melting process has sufilciently progressed for the 1imeusually employed in lump form-to have risen to the surface, silica, in the form of sand, refractory material, glass, or the like, is added in a larger amount than hitherto customary, infact, sufllcient to acidify the originally basic slag, and to form a slag with a concentration ratio of silica to lime that is best adapted to prevent migration of the manganese from the bath into the slag, and to reduce such manganese as has already passed into the slag, without permitting an; detectable return of sulphur and phosphorus from the slag into the bath. Investigations have proved this ratio to be best adapted at from 1 to 1.5 up to 1 to 2. By the process of the present invention therefore, subsequent additions of term-manganese are obviated, and the usual addition of ore, with its-in any eventundesirable introduction of oxygen. is rendered superfluous.

A further effect of the acidification of the, originally basic, slag by a copious addition of sand or the like, is to be seen in the decomposition of compounds of iron and oxygen in the slag and the resulting decrease in the iron content of the latter. This is equivalent to an increased yield of steel, in this process, as compared with that furnished by the existing processes for producing steel in ordinary Siemens-Martin furnaces.

Since the absorption of manganese by the slag is prevented in all the operations according to the present process, the latter also precludes the risk of inclusions-in the form of manganese sulphides or silicates-4n the finished steel. It also excludes the risk of alumina inclusions, by dispensing with the addition of aluminium. The injurious effect of such inclusions on the physical properties of the steel is sufilciently well known, and emphasises the advantages afforded by the present process.

A further advantage of the present process consists in that the increased fluidity of the slag through the addition of large amounts of-sand, or the like, allows all the reactions between the bath and the slag to proceed with the desired speed, so that there is no need for the addition of fluor spar, or similar material, which would increase the cost. I

The following examples represent: (A) the process according to the present invention; and (B) a current process. In both cases, the charges are intended to produce plate material.

Example A Charge Pig-ir 22000 kgs. Tube scrap 16900 Crop ends 12500 Strip scr p 3500 Tm'nina'a 7000 Bay scrap, waste material which is produced at the casting of steel blooms 5000 Caucasian washed manganese ore (52%) Ferrosilicon (78%) Total charge 67700 Yield 84360 Analysis: 0.22% C, 0.72% Mn, 0.21% Si, 0.031% P, 0.031% S;

ExampleB 12 Charge Pig-ir n 15000 1:8 Heavy melting scrap 16900 Strip scrap 6900 Plate sides and ends 23100 Tube scrap 5000 66900 Ferro-manganese (80%) 800 Ferro-silicon-alum'inium. 260

Total 67960 Yield 64860 Analysis: 0.19% c. 0.53% Mn, 0.14% si, 0.015% P, 0.033% s.

I The run took '1 hours 35 minutes. 3000 kgs. of lime were melted down with the charge, and about 1000 kgs. of lime and 500 kgs. of fluor spar were added later. The melt was desoxidized with ferro-manganese or ferro-silicon-aluminium.

The examples speak for themselves.

As is to be seen from Example A the slag is acidified to such a degree that the basicity of the slag is substantially decreased whereas it is not intended to transfer the original basic slag into an acid one. It will thus be understood that by acidifying referred to in the specification and in the claim it is only intended to characterize a process by which the basicity of the slag is suband the lime isfloatlng upon the surface, acidifying the basic slag thus formed and transferring the slagged manganese from the slag into the bath and finally tapping the melt after it has obtained the desired properties.

CARL WALL-MANN. FRITZ HALBROCK. EMIL KUMPMANN. 

